Process for improving the color of fats and fatty oils by treatment with chlorine dioxide



E COLOR OF FATS AND FATTY E. R. WOODWARD Flled Dec 23, 1948 OILS BY TREATMENT WITH CHLORINE DIOXIDE mm m w April 8, 1952 PROCESS OF IMPROVING TH i\) R O RG INWOR I716 Z dm/zaora ATTORNEYS Patented Apr. 8, 1952 PROCESS FOR IMPROVING THE COLOR OF FATS AND FATTY OILS BY TREATMENT WITH CHLORINE DIOXIDE Eric R. Woodward, New York, N. Y., assignor to Mathieson Chemical Corporation Application December 23, 1948, Serial No. 67,045

Claims.

The present invention relates to the bleaching of fats, fatty oils, and the like, by subjecting such materials to the action of chlorine dioxide gas. It is of particular utility in the bleaching of tallow and other glyceride esters by the general process described and claimed in my copending application Ser. No. 771,561 filed August 30, 1947, now Patent No. 2,473,930, of which the present application is in part a continuation. It is, however, also useful in the bleaching of non-glyceridic esters. It is of general utility in the bleaching of fatty esters, say those having at least 8 to 10 carbon atoms in the acid radical, for instance, tallow, cotton seed oil, corn oil, soybean oil, lecithin, beeswax, carnauba wax, candelilla wax, in fact, any of the mono-, di-, or tri-glycerides or mixtures thereof.

The treating of such materials, tallow, for instance, with a bleaching agent, is usually carried out in a large tank, many feet in diameter, and having a capacity of many tons. While the process of my above-identified application has been carried out with surprising success and economy in large tanks such as just noted, it is frequently necessary to take special precautions in order to effect a uniform treatment and avoid overtreatment of a portion of the tallow and undertreatment of a further portion. This has frequently necessitated the agitation of the tallow, for instance, throughout the treating period. Further, in operations of that sort, it is usually necessary to carry out the process batchwise.

My present invention provides an improved method of treating materials of the type noted with chlorine dioxide where previously experienced difficulties are avoided, which is adapted to continuous operation and whereby more uniform and accurate control of contact between the chlorine dioxide and all portions of the tallow are assured. The process of the present invention has the further advantages of greater economy in reagents and equipment, greater flexibility and more ready control.

The process has been used with particular advantage in the bleaching of tallow and, for simplicity, the invention will be described with particular reference thereto. It will be understood, however, that the utility 'of'the invention is not so restricted, but that it is applicable to the treat= ment of other oils and fats susceptible to bleaching with chlorine dioxide, especially other glyceridic esters. It is also useful in the bleaching of non-glyceridic esters.

In accordance with my present process, I pass the tallow through a conduit of relatively small cross-section and inject the chlorine dioxide in admixture with an inert gas into the flowin stream of tallow. Advantageously, the conduit is provided at its downstream end with a gas outlet for venting 01f any unconsumed gases. I prefer to arrange the conduit vertically in the form of a standpipe and to pass the tallow upwardly therethrough and, from thence, to a storage tank and to inject the chlorine dioxide into the upwardly flowing stream of tallow at an appropriate point along the standpipe, usually the lower end, so that the length of the conduit and rate of flow may be so coordinated as to give the desired time of contact. A number of inlets for chlorine dioxide may be arranged along the standpipe whereby the period of time may be adjusted independently of the rate of flow. With such arrangement, the chlorine dioxide may be injected at one point or it may be injected at two or more points along the standpipe.

Due to the explosive nature of chlorine dioxide gas, it is desirable that the chlorine dioxide be diluted by admixture with an inert gas, air, for instance, to a concentration such that the partial pressure of the chlorine dioxide in the mixture does not exceed millimeters of mercury. It may be generated, for instance, by passing a mix ture of chlorine gas and air in contact with sodium chlorite, the proportion of air in the mixture being so regulated as to effect the desired dilution of the resultant chlorine dioxide.

Though other inert gases, for instance, nitrogen or carbon dioxide, may be used as the diluent for the chlorine dioxide, I prefer to use air for this purpose. Concentrations of chlorine dioxide and air such that the partial pressure of the chlorine dioxide is within the range of one millimeter to 30 millimeters of mercury are particularly advantageous, the optimum chlorine dioxide concentration depending upon the particular material being treated, the extent of bleaching desired and the time of contact in the treating conduit. Generally, the bleaching action is accelerated by an increase in the chlorine dioxide concentration in the chlorine dioxide-air mixture. Concentrations of 5-25 millimeters partial pressure are generally preferable.

The proportion of chlorine dioxide used is likewise subject to considerable variation depending upon the material being treated and the results required. Generally, the C102 should not exceed 0.2% by weight on the fat. Greater proportions may result in overtreating the fat. Proportions as small as 0.02% may frequently be used with noticeable results. Smaller proportions are not usually of practical utility. Usually, the amount of chlorine dioxide used should be such that it is substantially completely consumed in passing through the treating conduit. Where a more rapid bleaching is required, larger proportions of chlorine dioxide may be employed, but with decreased economy with respect to the chlorine dioxide.

Optimum treating temperature will depend upon the characteristics of the material being treated. The temperature should be above the melting point of the material being bleached and in the treatment of tallow, the operating temperature r may, with :advantage, be within the range of 120 to'200 F. It will be appreciated that temperature and time of contact, as well as proportion and concentration of the chlorine dioxide,

are to a considerable extent interdependent.

The diameter of the treating conduit should be relatively small, that is, such that the tallow will flow therethrough at a substantially uniform velocity throughout the transverse area of the conduit, at least to the extent of minimizing-differences in the time for each portion of the tallow to pass through the conduit. Diameters as small as 2 inches have been used with advantage. Where the conduit is positioned vertically in the formofa standpipe, somewhat larger diameters are usually desirable. Stan'dpipes of 6 inches in diameter have 'been used with advantage, but

'standpipes of smaller and larger diameters may be employed, depending primarily upon the intended rate of flow. Either straight or spiral conduitsmay be used, the latter sometime being desirable where space is the major consideration.

The invention is especially useful in the'treating oftallow, or the like, as it is delivered to the plant from tank cars, or other transporting vessels. It is, however; of broader application. For instance, tallow may be withdrawn from large storage or treating tanks such as conventionally used, 'passed through the treating conduit in contact'with the chlorine dioxide and returned tostorage or other suitable receptacle. It is applicable either to once-through or cyclic operation. By :once-through operation, I mean one in which the'treatment is completed-during aJsingIe passage through the treating conduit. By'cyclic' operation, I mean one in which the tallow is repeatedly circulated through the treating conduit in contact with the chlorine dioxide.

Theinvention will be further described with reference to the accompanying drawing which represents conventionally and diagrammatically an embodiment of the invention in which tallow isbleached while passing upwardly through a standpipe.

It will be. understood'that the drawing is purely diagrammatic-and is not intended to be drawn to. scale.

.Inthe accompanying drawing, the standpipe isindicated by the reference numeral 1. 'In one method. of operation, tallow, at a temperature at which it isfluid ispumped. from a tank car, not shown, through conduit 2 and passed upwardly through the standpipe or treating. conduit I. A

mixture of chlorine dioxide and air, from any convenient source, is passed to the system through conduit 3-and.injected into the lower end of the standpipethrough valve connection 4. The mixture of .chlorine dioxide andairpasses upwardlythroughthe standpipe, together with the tallow and bleaching of the tallow is thereby effected.

,-At the upper end of the standpipe,.the. air and any unconsumed chlorine dioxide are withdrawn through thevalvedvent 501' the standpipe may be open to the atmosphere -at its upper end. The .tallow is withdrawn through line 6 and passedto any one of the storage tanks I, B or -9,through valved connections III, II or I2, respectively, by appropriate manipulation of the valves in those connections and valves- I3,- I4 and I5 in line:6. Wheredesired, the treated tallow mayrbe conveyedthrough line 6 to any other storagerfacilitybr places of use by closing the valvesiinlines I0, II and I2 and opening valves I3, I4 and I5. The tallow may be withdrawn *from'the'tanks '-'I, 8 an'd9, as desired, through valved connections I6, I'I-and I8, respectively, and line I9.

In another method of operation, the tallow .may be-withdrawn from one of the storage tanks, passed upwardly through the standpipe and, from thence,.to' a second storage tank. For instance, assuming tank I to contain tallow to be bleached and'tank's to be empty, the unbleached tallow is withdrawn from tank I through valved connection 20 and line-2| and by means of centrifugal pump 22 is forced upwardly through the standpipe I, the valve in line 2 being closed. A mixture of chlorine dioxide and air is injected into-the lower end of the standpipe, as previously described. The'air and'any excess chlorine dioxide -are withdrawn through vent 5 and the bleachedtallow' passed from the upper end of the standpipe through lines and valved connection- II into tank 8, valve I4 and the valve in connection I0 being closed.

Tanks 8 and 9 are, likewise, provided with valved connections 23 -and'24, respectively, leading to line 2| whereby tallow from any one or more of the storage tanks may be passed to the-standpipe for treatment. Also, tallow from any'other' source may be passed to the system through valve25 in the extension of line 2I.

Instead'of passing all of the chlorine dioxide into the lower end of standpipe I through valved connection 4, all, or a portion thereof, may be passed to the'standpipe through valved connections 26, 21 or 28, many combination thereof.

The invention will be further illustrated by the-following specific examples of its application to the bleaching of tallow.

Example I Tallow at a temperature of to 200 F was pumped upwardly through a standpipe of 6 inches diameter and passed from the upper end thereof to 'a storage tank through a 2 inch line leading off from the standpipe at a point 2 feet from the top thereof. The tallow was passed through the standpipe, which was 17 feet high, at a rate of 15 gallons per minute. A mixture of chlorinedioxide and air, of which the partial pressure of chlorine dioxide was approximately 25 millimeters of mercury, was injected into the standpipe near its base at the rate of 400 cubic feetper hour. Air and excess chlorine dioxide wereseparated from the tallow at the upper end of the standpipe and vented to the atmosphere. The time of contact of the chlorine dioxidewith theitallow in passing through the standpipe was approximately 1.8 seconds and during this time, the tal-low was bleached from FAC 39 to FAC 21.

Example II "'In an operation substantially identical with that of "Example I except that the tallow was passed'through the standpipe at a rate of 10 gallons per .minute, the tallow was bleached from.FAC 39'to-FAC 19, time of contact of the chlorine dioxide with the tallow in this case being approximately 2.7 seconds.

Example I I I Tallow at a temperature at which it was liquid waspumped from a tank car into a storage tank through a 2 inch conduit. A mixture of chlorine dioxide and air, of which the partial pressure of chlorine dioxide was approximately 27 millimeters of mercury, was injected intothe conduit on the discharge ide of the pump at a point about 45 feet from the storage tank. The tallow was passed through the line at the rate of 64% gallons per minute and the mixture of chlorine dioxide and air was injected into the conduit at the rate of 400 cubic feet per hour. The time of contact between the chlorine dioxide and the gas in passing through the conduit was approximately 9 seconds and during this period, the tallow having an initial FAC color of 13, was bleached to FAC' dark 5.

The process is especially applicable for improving the color of esters of long chain fatty acids containing but minor proportions of free fatty acids, not exceding about 10% by weight, and in which both the fatty material and the gas mixture are substantially dry and free from mineral acidity. However, in its broader aspect, the present invention is not so limited, but is applicable generally to the treatment of fatty materials of the type hereinbefore described, either in the crude, or the partially refined condition. I have found palm oil, for instance, to be especially susceptible to rapid bleaching by treating with chlorine dioxide in accordance with my process and to be readily bleached from a dark red color to a light yellow color by the continuously once-through method of operation.

Because of the accurate control of contact time provided by the present process, the proportions of the reagent to the material to be bleached, may be relatively greater than that ordinarily used in the bleaching of similar materials in large bodies. Accordingly, the rate of bleaching may be materially accelerated without fear of overtreatment, or deleteriously afiecting the fatty material. Also, by my process, the presence of moisture or relatively large porportions of free fatty acid is less objectionable and difiiculties due to color reversion are minimized. However, for most advantageous operation, it is'important that any water present in the material to be bleached not exceed about 2% by weight, preferably not over By injecting the Cl02-air mixture into the flowing stream of the material to be bleached. the gas becomes rapidly and uniformly dispersed therein. Usually, no other provision for promoting mixing is necessary, especially where the stream is flowing, at a relatively high velocity. However, means for dispersing the gas in the stream of liquid may be employed if desired, and may at times be used with advantage, especially if the velocity of the liquid stream is quite low.

The invention and its effective application to various other fats and fatty oils will be illustrated by the results of a number of runs carried out on a laboratory scale.

The difierence in susceptibility of the various materials to color improvement by my present process is emphasized by the use of relatively low partial pressures of the chlorine dioxide in air.

In each of these additional runs, except the first (Example IV), the chlorine dioxide was mixed with air and the partial pressure of the chlorine dioxide was 7.6 mm. of mercury. In Example IV, the partial pressure of chlorine dioxide was 4.8 mm. of mercury.

In each run, the material to be bleached was passed through a water or steam jacketed glass tubing at the rate of 25 cubic centimeters per minute. At this rate, it required about '7 seconds for a single once-through pass of the gas 6 and material to be bleached through the tube. The fatty material being introduced to the tube was, in each instance, in a liquid state and liquid conditions were maintained throughout the tube. The chlorine dioxide-air mixture was continuously charged to the inlet of the tube wherein it was intimately mixed with the fatty material and passed together with the fatty material through the tube. The proportion of the gas mixture to the liquid charged to the tube was, in each instance, equivalent to about '7.5 10- grams of chlorine dioxide per gram of the fatty material being bleached. The liquid passing from the tube was collected in a vented receptacle to permit separation of the gases from the fatty material and the fatty material.

together with additional chlorine dioxide-air mixture was recycled through the tube.

Example IV Cottonseed oil having an FAC color of 11A was passed twice through the apparatus'at a temperature of approximately 75 (3. (167 F.) together with a chlorine dioxide-air mixture in which the partial pressure of the chlorine dioxide, as previously noted, was 4.8 mm. of mercury. By this treatment, the FAC color of the oil was reduced to 5.

Example V Soybean oil having an FAC color of 11C was passed 8 times through the apparatus previously described while maintained at a temperature of about 75 C. together with chlorine dioxide-air mixture in which the partial pressure of the chlorine dioxide, as previously noted, was 7.6 mm. of mercury. By this treatment, the FAO color of the soybean oil was reduced to 9.

Example VI A sample of mixed methyl esters of rice bran fatty acids having an FAC color of 41 was cycled ten times through the apparatus, the tube being heated by passing atmospheric steam through the surrounding jacket. By this treatment, the FAO color of the fatty material was reduced to 33.

Example VII A sample of lecithin having an FAC color of 43 was cycled fifteen times through the apparatus under the conditions of Example VI and, by this treatment, its FAC color was reduced to 37.

Example VIII A sample of diethylene glycol laurate was cycled three times at room temperature and its Lovibond color of 12 red and '70 yellow was improved to 1.3 red and 35 yellow.

Example IX A sample of mono-oleate of polyethylene glycol having a molecular weight of about 400 was given 10 passes through the apparatus at room temperature and thereby the Lovibond color was improved from 18 red and 35 yellow to 8 red and 20 yellow. v

It will be appreciated that time of contact, tem-- perature and concentration of the chlorine dioxide are, to a major extent, interdependent and, accordingly, the contact time may be materially reduced by increasing the chlorine dioxide concentration within the limits heretofore specified.

I claim:

1. In the process for improving the color of fats and fatty oils in which the material to be bleached is treated by passing a mixture-of chlorine dioxide and an inert diluent gas in contact therewith, the steps comprising'flowing the material to be bleached as a stream of relatively small transverse area through an elongated, confining conduit injecting the mixture of chlorine dioxide and diluent gas into the flowing stream, and bleaching'the material to the desired color by-correlating the rate of flow of the material to be bleached with the injection of the chlorine dioxide mixture in a manner limiting the period of contact between the material to be bleached and the chlorine dioxide to a very short contact period in contrast to that of tank bleaching.

2. In the process for improving the color of fats and fatty oils in which the material to be bleached is treated by passing a mixture of chlorine dioxide and an inert diluent gas in contact therewith, the steps comprising flowing the material to be bleached as a stream of relatively small transverse area through an elongated, confining conduit, injecting the mixture of chlorine dioxide and diluent gas into the flowing stream, bleaching the material to the desired color by correlating the rate of flow of the material to be bleached with the injection of the chlorine dioxide mixture in a manner limiting the period of contact between the material to be bleached and the chlorine dioxide to a very short contact period in contrast to that of tank bleaching and separating the inert gas and residual chlorine dioxide from the fatty material at the downstream end of the conduit.

3. In the process for improving the color of fats and fatty oils in which the material to be bleached is treated by passing a mixture of chlorine dioxide and an inertdiluent gas in contact therewith, the steps comprising flowing the material to be bleached upwardly through an elongated, vertically positioned, confining conduit of relatively small transverse area, injecting a mixture of the chlorine dioxide and the diluent gas into the lower end of the conduit in contact with the flowing stream, bleaching the material to the desired color by correlating the rate of flow of the material to be bleached with the injection of the chlorine dioxide mixture in a manner limiting the period of contact between the material to be bleached and the chlorine dioxide to a very short contact period in contrast to that of tank bleaching, separating the diluent gas and any residual chlorine dioxide from the fatty material at the upper end of the conduit and separately withdrawing the separated gas and fatty material therefrom.

4. In the process for improving the color of tallow in which the tallow is treated by passing a mixture of chlorine dioxide and an inert diluent gas in contact therewith, the steps comprising flowing the tallow as a stream of relatively small transverse area through an elongated confining conduit, injecting the mixture of the chlorine dioxide and diluent gas into the flowing stream,

and bleaching the material to the desired color by correlating the rate of flow of the material to be bleached with the injection of the chlorine digated, vertically positioned, confining conduit of relatively small transverse area. injecting a mixture of the chlorine dioxide and the diluent gas into the lower end of the conduit in contact with the flowing stream, bleaching the material to the desired color by correlating the rate of flow of the material to be bleached with the injection of the chlorine dioxide mixture in a manner limitting the period of contact between the material to be bleached and the chlorine dioxide to a very short contact period in contrast to that of tank bleaching, separating the diluent gas and any residual chlorine dioxide from the tallow at the upper end of the conduit and separately withdrawing the separated gas and tallow therefrom.

6. The process of claim 1 in which the proportion of chlorine dioxide is within the range of 0.02% to 0.2% based on the weight of the material being bleached.

7. The process of claim 1 in which the material being treated does not contain more than 2% of water by weight.

8. The process of claim 1 in which the material being treated does not contain more than water by weight.

9. In the process for improving the color of fats and fatty oils in which the material to be bleached is treated by passing a mixture of chlorine dioxide and an inert diluent gas in contact therewith, the steps comprising flowing the ma terial to be bleached as a stream of relatively small transverse area through an elongated, confining conduit, injecting the mixture of chlorine dioxide and diluent gas into the flowing stream, and bleaching the material to the desired color by correlating the rate of flow of the material to be bleached with the injection of the chlorine dioxide mixture in a manner limiting the period of contact between the material to be bleached and the chlorine dioxide to a very short contact period within the range of about 1.8 seconds to about 105 seconds.

10. In the process for improving the color of fats and fatty oils in which the material to be bleached is treated by passing a mixture of chlorine dioxide and an inert diluent gas in contact therewith, the steps comprising flowing the material to be bleached as a stream of relatively small transverse area through an elongated, confining conduit, injecting the mixture of chlorine dioxide and diluent gas into the flowing stream, bleaching the material to the desired color by correlating the rate of flow of the material to be bleached with the injection of the chlorine dioxide mixture in a manner limiting the period of contact between the material to be bleached and the chlorine dioxide to a very short contact period within the range of about 1.8 seconds to about 105 seconds, and separating the inert gas and residual chlorine dioxide from the fatty material at the downstream end of the conduit.

ERIC R. WOODWARD.

REFERENCES CITED "The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,224,984 Potts et al Dec. 17, 1940 2,269,667 Kauffman Jan. 13, 1942 2,327,569 Thurman Aug. 24, 1943 2,473,930 Woodward June 21, 1949 

1. IN THE PROCESS FOR IMPROVING THE COLOR OF FATS AND FATTY OILS IN WHICH THE MATERIAL TO BE BLEACHED IS TREATED BY PASSING A MIXTURE OF CHLORINE DIOXIDE AND AN INERT DILUENT GAS IN CONTACT THEREWITH, THE STEPS COMPRISING FLOWING THE MATERIAL TO BE BLEACHED AS A STREAM OF RELATIVELY SMALL TRANSVERSE AREA THROUGH AN ELONGATED, CONFINING CONDUIT INJECTING THE MIXTURE OF CHLORINE DIOXIDE AND DILUENT GAS INTO THE FLOWING STREAM AND BLEACHING THE MATERIAL TO THE DESIRED COLOR BY CORRELATING THE RATE OF FLOW OF THE MATERIAL TO BE BLEACHED WITH THE INJECTION OF THE CHLORINE DIOXIDE MIXTURE IN A MANNER LIMITING THE PERIOD OF CONTACT BETWEEN THE MATERIAL TO BE BLEACHED AND THE CHLORINE DIOXIDE TO A VERY SHORT CONTACT PERIOD IN CONTRAST TO THAT OF TANK BLEACHING 